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C.Z. osecrans 


An Ex ] 
perimental Study OF The Explosions 


Of Gaseous Mixture 


AN EXPERIMENTAL STUDY OF THE 
EXPLOSIONS OF GASEOUS 
MIXTURES 


BY 


CRANDALL ZACHARIAH ROSECRANS 
B. S. University of Illinois 
1919 


THESIS 


Submitted in Partial Fulfillment of the Requirements for the 


Degree of 


MASTER OF SCIENCE 
IN 


MECHANICAL ENGINEERING 


THE GRADUATE SCHOOL 


OF THE 


UNIVERSITY OF ILLINOIS 


atau 40S 


HE OLEO, irom 


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UNIVERSITY! OF ILLINOIS 


THE GRADUATE SCHOOL 


I HEREBY RECOMMEND THAT THE THESIS PREPARED UNDER MY 


SUPERVISION BY CEANDA 


ENTITLED____AWN 


OF GASEOUS MIXTURES. 


BE ACCEPTED AS FULFILLING THIS PART OF THE REQUIREMENTS FOR 


THE DEGREE OF MASTER 


; - In Charge of Thesis 


Head of Department 


Recommendation concurred in* 


Committee 


on 


Final Examination* 


*Required for doctor’s degree but not for master’s 


Digitized by the Internet Archive 
in 2015 


https ://archive.org/details/experimentalstud0Orose 


CONTENTS 


Introduction . . . .« «6 « . 
Review of Previous Researches . 
Description of Apparatus . . . 
Procedure in Meking an Explosion 


OO a ee a 


Genelu@ions ..-. +6 -« « e« e 


BpVGRGte =. 5s Ss «© «© © 


of Figures 


Clerk é 
Clerk ‘ 

Grover . - 
Grover . . 

Bairstow & Alexander 
Bairstow & Alexander 
Bairstow & Alexander 
Hopkinson's Explosion V 
Hopkinson . 
Hopkinson . 
David at eG 


e ° e « e . e 


odBwIOmpP Gwe 
Mm 
a7) 


David ° : 
David P 
Cylindrical Vessel 
Conical Vessel ‘ 
Hemispherical Vessel 
L-head Vessel. . . 
Original Indicator . 
Manometer and Connections 
Drawing of Apparatus oe 
Photograph of New Indicator 
Calibration Curve for Indicator 
Photograph of Remodeled Apparatus 
Photograph of Remodeled Apparatus 
Gas and Air Piping . ... . 
Ignition Wiring Diagram ° 0 
Facsimile of Explosion Card ° 
Series at Vip ° a 
Series ° 

Series ee 

Series ° 

Series P 

series 


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Series : 
Series Fi 
Series y 
Series é 
Series ‘ a 


Series 

series 

Series 

Series 

Series 

Series 10 and 11 
Series 12 . . 
Series 13. . 
Series 12 and 13 
Series 10, 11, le, and 
Series 14. . a 
Series 2, 8, 10, and 14 
Effect of Ratio of Surface 
Cooling Curves ° +; Cus 
Curves of Temperature Drop 
Explosions of Hydrogen and Air 
Explosions of Hydrogen and Air 
Explosions of Hydrogen and Air 
Curves of Energy and Equilibrium 
Manetione -. .« + « «© « -e 


6 . . . e . es e . 


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eis 


AN EXPERIMENTAL STUDY 
OF THE 
EXPLOSIONS OF GASEOUS MIXTURES 


Purpose and Scope of Investigation. 
The purpose of this investigation is the study of 


I. Introduction. 
some of the physical phenomena involved in the explosions of 
gaseous mixtures in a closed vessel. The problems connected 

with the chemical changes involved, or any of the other in- 
cidental problems arising, have not been considered within the 
scope of this investigation. 

It is the purpose of this discussion to point out 
Various comparisons existing between explosions taking place 
in different shaped vessels. These vessels were designed to 
simulate the various forms of combustion spaces actually in 
use in modern gas engines. 
Acknowledgments. 

The writer is indebted to A.P.Kratz, Research 
Assistant Professor in the Department of Mechanical Engineer- 


ing, for much of the apparatus employed in this investigation 


ay 


t 
3 


| 


es well as for his supervision of the present investigation. 
The apparatus was designed and milt by Professor Kratz dur- 
ing the years 1915-1916, and some of the preliminary reswlts 
were obtained by him. These results are embodied in this 
discussion, as hereinafter noted. The apparatus wes then 
remodeled, and additional results obtained by the writer. 
Generel Consideration of Explosions in a Closed Vessel. 
Consider a homogeneous mixture of any inflammable 
gas aid air enclosed in 2 vessel with heavy metallic walls. 
The gas is assumed to be at atmospheric temperature, as is 
also the vessel. If an igniting sgent, such as an electric 
spark, be communicated to the gas mixture, inflammation will 
take place, more or less rapidly, according to the nature of 
the mixture. The heat developed by the combustion will raise 
the temerature of the gases, and hence the pressure in the 
vessel. At the same time the gas is losing heat to the cold 
wall of the vessel. This loss of heat reduces the heat 
available for raising the pressure of the gas. At an instant 
when the loss of heat to the walls exactly bulances the heat 
developed from the commstion, the pressure ceases to rise. 
This point on the pressure curve may be known as the "maximum 
pressure". The gas then cools slowly, by losing heat to the 
walls of the vessel, which, owing to its large mass in com- 
parison with the mass of the gas, does not become appreciably 
heated. The pressure of the gas decreases as this cooling 


process goes on, and finally attains the original pressure 


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of the gas mixture,as charged into the vessel, but with any 


slight difference which might be caused by the contraction 


or expansion of the gases due to the chemical combination. 

The time elapsing from the instant of ignition 
(that is, of the passing of the spark) to the instant of at- 
taining maximum pressure will be designated as the "time of 
explosion”. The ratio of air to gas, by volume, as origi- 
nelly charged into the vessel, will be known as the “air-gas 
vanio"; or "RB". 

It is the pumyose of this discussion to canpare the 
Maximum pressures developed and the times of explosion for 
different mixtures, exploded in different shaped vessels. 

An estimate will also be made of the amount of heat 


lost te the walls of the vessel during the time of explosion. 


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II. REVIEW OF PREVIOUS RESEARCHES 


There has been 2 considerable amount of experi- 
menting done on the physical phenomens involved in the ex- 
plosions of gaseous mixtures. The work of some of the 
experimenters in this field will be discussed in the fol- 
lowing peragreaphs. 


Dugald Clerk! 


In 1884 Clerk exploded mixtures of Cambridge coal 


gas and air at various initial pressures and temperatures. 

His explosion vessel was cylindrical in form and 
had ae volume of 317 cubic inches. The pressure developed in 
the cylinder was measured by means of a Richards indicator, 
and the pressure diagrams were traced on a revolving drum. 
Jump epark ignition was used, with the spark occurring at the 
bottom of the cylinder. Explosions of hydrogen and air were 
also made in the same apparatus. 

In a later series of experiments a cylinder 7" long 
end 7" in diameter was used. The Richards indicator was re- 
tained, but a slide, moving longitudinally, was substituted 


for the dmn. The recording paper was fastened to the slide, 


1 Dugald Cle rk--The Gas, Petrol, and Oil Engine, p. 126. 


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and the slide wes calibrated by means of m electrically driven 
tuning fork (having a frequency of 200 vibrations per second) 
which traced a curve on the recording paper. 

Clerk's curves, Smwirg the relation between maxi- 
mum pressure end sir-ges ratio, and time and sir-gas ratio 
ere typical of all experiments in the field, and are reprw- 
duced in Fig. l. A set of actual explosion curves for dif- 
ferent air-ges ratios (taken with the later apparatus) is 
shown in Fiz. ¢&. 

Clerk's results are the best of those obtained from 
the early experimenters on gas explosions, tut they ere in 
error on eccount of the inability of the indicator to follow 
the rapid changes of pressure. 

Massachusetts Institute of Techm logy! 

Experiments similer to Clerk's were conducted at the 
Maseachusetts Institute of Technology in 1898. The apparatw 
employed was similar to that used by Clerk, except tht a ro- 
tating dise was used as the recording device. The pressures 
were therefore plotted on polar, instead of rectmegular, co- 
ordi nates. 

The resulte closely approximte those obtaimd by 
Clerk and confirm all of his conclusions. 

Experiments were also mde with this apparatus on 
mixtures of gasoline vapor and air. 


— 0 oe ee ee eee ee ee eee ee me me ee ee ee ee ee 


1 clerk--The Gas, Petrol, m4 Qil Eine, p. 148. 


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Grovert 

In 1895 F. Grover sagecuieme experiments on the ex- 
plosions of mixtures of coal gas and airinan gparatus much 
the same as Clerk's. The explosion vessel td a volume of 
one qmbic foc. It was 8" in diameter and 34" long. A 
Crosby indicator was used to determine the pressure developed, 
and a tuning fork to record the time. The mixture was in- 
troduced by filling the cylimer with water, and allowirg the 
gas and air to enter as the water flowed out. 

The results of Grover's work,when explosion (or max- 
imum) pressure wes plotted against the air-gas ratio, gave 
curves falling much below tmwse obtained by Clerk and at the 
Massachusetts Institute of Technology, although the calorific 
walue of the gases was practically the same in all cases. 
Grover accounts for this difference by the fact that the heat 
taken to evaporate the water adhering to the cylinder walls 
after drawing in the gas charge reduced the heat available for 
raising the pressure. It is probable, however, that his 
method of introducing the mixture was not as conducive to 
tho rovgh mixing as the method used in Clerk's researches. It 
is a well known fact that a lean mixture will ignite much more 
rapidly if a small amount of relatively strong mixture is 
situated in the immediate vicinity of the ignition point. The 
time of explosion was shorter in Grover's wrk than in the 


——_ eww ee ee Ew ee Se Oe Se Ee ee Ee eee ee ee 


1 Clerk--The Gas, Petrol, ad Oil Engine, p. i153. 


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previously described experiments, in almost every case, and 
this fact seems to indicate that the lower pressures developed 
in Grmver's experinents were me to faulty mixing of the 
charge. 

Grover also made explosions with mixtures consisting 
of coal gas, air, and exhaust gas left from the preceding 
explosion. His results indicated that the presence of from 
5% to 30% of extaust gas in the initial gaseous mixture 
actually raised the pressure as much as 19 lb. per sq. in. 
above that cserved for a mixture containing the sane per- 
centage of fresh coal gas. This apparent increase of mexi- 
mum pressure became less as the strength of the mixture in- 
creased, and with a 12 to 1 mixture the effect became negli- 
gible. With a 7 to 1 mixture the maximum pressure was 
decreased by the presence of exhaust gas. This fact, to- 
gether with an analysis of the exhaust gas, proved conclu- 
Sively that the imrease of pressure with the weaker mixtures 


was due to the fact that the exmust gases contained as high 


as 30% of inflammable gases remaining from the previous in- 


comple te combus tion. The obvious conclusion is that the 
products of commstion, unless they contain unburred gases, 
cannot raise the explosion pressure when used as a diluent. 

Grover later (1898) made explosions of acetylene 
and air mixtures, using the same experimental apparatws. The 
gas, however, wes measured in from a gas holder, and the 


error me to the water left in the cylinder was thereby 


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eliminated. Low tension make md break ignition was used, 
the spark occurrirm at the center of the cylinder. 

The mixtures were exploded at 1, 2, md 3 atmos- 
pheres initial pressure. (Mixtures of coal gas and air were 
@lso exploded at the same initial pressuref)- The results, 
however, still show evidence that a perfectly homogeneous 
mixture was not obtained, as the coal gas explosion pressures 
are again low as compared with Clerk's. 

Curves of explosion pressure plotted against initial 
pressure are given in Fig. 3. From these curves it is evident 
that the explosion pressure increases almst directly as the 
initial pressure. The deviation from a straight line law may 
be explained by the poor mixing of the charge evident in all 
Grovyer's work, since the straight line law was confirmed by 
later experimenters. 

Curves of pressure and time of explosion for dif- 
ferent mixtures of acetylene and air,and coal gas and air are 
given in Fig. 4. 

Petavelt 

Petavel's experiments (1902) on the explosion of 
gaseous mixtures are of great interest, as they are the only 
ones carried out at very high initial pressures. A spherical 
steel bomb having an internal diameter of 4" md a volume of 
0.0195 cu. ft. was used. 


eee re ene ee ee mm ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee ee oe ee 


1 Memoirs of Manchester Lit. ami Phil. Soc. v. 46, 
vert ©, p- Le 


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Petavel's indicator was a great impmvement on those 
used before. A steel tube, ending ina piston, am loaded as 
@ hollow column was used as the spring, md the motion was 
greatly magnified by a system of levers and a mirror. ‘The in- 
strument wes practically free from all inertia effects, and 
seemed to be able to follow the rapid pressure variations 


without appreciable lag. 


Bairstow and Alexander+ 


Explosion experiments were made in 1905 by Messrs. 
Bairstow and Alexander, using mixtures of coal gas and air. 
Their apparatus was exceedingly complete, and provisions were 
made for the most accurate measurenents possible. The in- 
dicator, a Similex, of the ordinary steam engine type, was, 
as ugaal, the weakest part of the apparawms. The exp losion 
vessel was 18" lmg and 10" in diameter, and had a volume of 
0.821 cu. ft. The gas used the the city illuminating gas, 
and it averaged 628 Btu. per cu. ft. in heating value. 

Bairstow and Alexander found the same difficulty in 
getting a perfectly homo geneous mixture that Grover did. 
Mixtures were alloved to stand as lmgas 17 hours without 
diffusing enmgh to be ignited. A mixing plate, operated by 
hend,was therefore added. Igni tion was accomplished by 
means of a jump spark, through a "firing tube". This tube 


extended some distance down into the interior of the vessel, 


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14 


and was pierced with small holes at intervals. The electri- 
cal ignition device was situated at the top of the tube. All 
holes in the tube were plugged except one located at the de- 
sired distance from the top of the cylinder, and the electric 
igni tion spark was passed. The mixture in the tube exploded, 
throwing a jet of flame into the main part of the explosion 
vessel through the hole in the firing tube, and igniting the 
whole mixture. The position of the open Mle in the tube was 
changed to give ignition at any desired point of the vessel. 

Ignition accomlished by this means was not can- 
Stant in igniting power, as the greater amount of gas exploded 
in the firing tube when the lower hole was open pm jected a 
jet of flame farther into the main vessel than it did when 
the upper holes were open. This caused some variation in 
the maximum pressures and times of explosion of the mixtures 
in the vessel, due to the change in igniting power of the 
firing tube. With electric ignition, the spark gap being 
placed at the desired point in the vessel, this effect is 
eliminated. 

Fig. 5 shows the time of explosion md the maximum 
pressure as affected by the position of the ignition point, 
a7 to 1 mixture being wed in all the experiments. The 
initial pressure was 35 1b. per sq. in. absolute. Similar 
experiments were nmede with a weaker mixtwre, in which case it 
was found that the position of the ignition point for most 


rapid combustion was about three inches below the center of 


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16 


the vessel. This can be accounted for by the fact that the 
ecavection currents in the weaker mixture are suffici ently 
rapid to be comparable with the rate of inflammation. The 
position of the ignition point in the lower part of the vessel 
assists the convection mrrents. 

In all the following emerinents made by Bairstow 
and Alexander, four sparks in series, passing through the 
axis of the cylinder were used. Two complete series of tests 
were made, With varying mixtures, one series at 55 1b. per 
Sq. in. absolute initial pressure, md the other at 34.5 lb. 
per sq. in. absolute. The results are plotted in Fig. 6. 

It is questionable wnether the results of the ex- 
periments on ignition et different points of the vessel are 
very accurate or significant, since the variation in the ig- 
niting pover of the firing tube, as pointed out above, might 
cause a wide variation in the maximum pressure amd the t ime 
of explosion. 

The results of the pressure exp@inents as shown in 
Fig. 7 indicate clearly that the maximum pressure is directly 
proportional to the initial pressure (absolute). Further data 
on the cooling of various mixtures after explosion were given 
by these experinenters. These data will be discussed later. 
Fenn 


In 1900 Robert H. Fenn, working at the Clarkson 


? Engineering News, v. 44, pe. 366. 


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School of Technology, exploded mixtures of acetylene and air, 
and gasoline vapor md air in a cylimer with a mveable 
piston. His results merely confirm those heretofore given, 
especially in regard to the relation of maximum pressure to 
initial pressure. 

Bairstow and Horsely? 

During the year 1902 Bairstow am Horsely ran a 
series of explosions at two different initial pressures. Tre 
results seem to indicate that the explosion pressures are not 
exactly proportional to the initial pressures for the same 
mixture, but that the ratio of explosion pressure to initial 
pressure increases slightly with the increase of initial 
pressure. The se explosions were made in the same apparatus 


which was used by Bairstow and Alexander. 


Hopkinson® 


Perhaps the mst importmt am cmclusive researches 
in the field were made by the late Professor Hopkinson, of 
Cambridge. His researches were made with Cambridge coal gas, 
in a comparatively large cylinder (6.2 cu ft. in volume). 
Experimats were made with 9 to 1 and 12 to 1 mixtures, using 
gases saturated with water vaor inall cases. 

Hopkinson's original optical indicator was used in 


all this work, mdwas the first instrunent to be employed 


1 Engineering, v. 
2 


Cle rk>-The Gas, Petrol, and Oil Engine, p. 185. 


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20 


which was without dmbt capable of following the rapid var- 
iations of pressure during the explosions. For a detailed 
description of this indicator, reference may be made to the 
Hopkinson also measured the temerature of the 
burning gases by means of platinum resistmce thermometers 
inserted at different parts of the vessel, as shown in Fig. 8. 
The time lag of the thermometers was determined by separate 
experiments and corrections were applied to the results. The 
thermometers consisted of short coils of platinum wire 0.001" 
in diameter, @nnected in a galvanomter circuit in mcha 
way thet the change in resistmce due to the change in tem- 
perature caused a variation in the qmrrent in the galvanometer, 
and therefore caused the galvamne ter mirror to deflect. 
Records of temperature and pressure were taken on a photo- 
graphic film, fastened on a revolving dimm. The thermometers 
were placed as follows:- one at 50 cm. from the ignition point; 
and one very near the wall of the vessel. The center coil 
was almost invariably melted when the cherge was fired, in- 
dicating that the temperature near the ignition point was at 
least as high as the melting point of platinum (1755 deg. C). 
Fig. 9 shows the curves of temerature at the center of the 
vessel, and pressure, plotted against time. It my be noted 
that the platinum wire melted about 0.025 sec. before the 
attainnme nt of maximum pressure. The temperature at the start 


of inflammation rose r@idly. This indicated that the 


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— Hophinsons Explosion Vessel 


Lgnition Point 
Fresistance Thermometer at center 


id . JO crn. From wall 


“ “ / 


Yo/ume of vessel* 0684 cu.77. 


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combustion of the mass of gas near the ignition point was 
practically complete before the pressure had increased more 
than two or three pounds (as shown by the indicator). 

The flame then spread through the mixture with a 
velocity of approximately 150 cm. per second, and completely 
filled the vessel about 0.03 sec. before the attainment of the 
maximum pressure. This was shown by the fact that the tem- 
perature as recorded by the thermometer pleced 1 cm. from the 
walls attained a maximum about 0.03 sec. before the pressure. 
The gas et the center was then compressed adiabatically to a 
temperature considerably above the melting point of platinum, 
probably about 1900 deg. C. 

At the moment of maximum pressure the temperature 


distribution was approximately as follows;- 


Mean (calculated from pressure)..1600 deg. C. 
Center, near spark .......i4i1900 " B 
10 cm. within wall... . 
1 cm from wall at end . « 1200 


» L700 
1 em from wall at side - 850 

It is evident that even if the experiments were per- 
formed in a nonconducting vessel, differences in temperature 
would exist at different parts of the vessel, due, not to the 
conduction end radiation phenomena, but to the different de- 
grees of comression existing at the different points of the 
mixture. 

At a time 0.05 sec. later than the attainment of 


maximum pressure, the mean temerature of the gas, calculated 


from the pressure, was about 1100 deg. C. The mean 


re A 
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temperature {exclusive of a layer 1 cm. thick at the walls) 
was determined by a long platinum wire stretched entirely 


across the vessel. This temperature was found to be 1160 


deg. C., a value reasonably close to the calculated mean value. 


In the explosion of a weaker mixture (12 to 1), con- 


vection became more important die to the fact that the flame 


was propagated more slowly. The temperature immediately below 


the spark at first rose, then decreased as the cold unburned 


‘gasea moved upward following the ascending flame. One second 


after ignition the pressure was still less than 10 lb. per sq. 


in., and the upper half of the vessel was filled with mrned 


The last portions 


gas which was losing heat to the walls. 


of gas to be ignited were those immediately below the spark. 


In the 12 to 1 mixture the maximum pressure was 


about 50 lb. per sq. in. and was attained <.5 sec. after ig- 


nition. During half of that time at least half of the super- 


ficisl area of the vessel had been in contact with the flame. 


Thus the loss of heat before the attainment of maximum pres- 


sure was probably greater in a weak mixture than in one of 


greater strength. 


In some subsequent experiments Hopkins undertook to 


measure the heat loss to the wall. For these experiments he 


used a cast iron cylimer 1 foot in diameter and 1 foot long, 


which was lined with wood. The wood was overlaid with a con- 


tinuous grid of strip copper, 4" wide and 0.04" thick, which 


was connected by wires to a galvanometer circuit, in order to 


? ben Lone ¥} 


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ed he it 


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record the change in resistame of the strip as it was heated 
by the explosion. The record of the changes in resistmce 
was photographed on a film, together with the pressure curve 
from the Hopkinson optical indicator, The results of cal- 
culations based on the data obtained are shown in Fig. 10. 
Hopkinson says, "The heat loss begins about 0.05 sec. after 
ignition, when the flame first comes in contact with the copper. 
At first the loss goes on at avery great rate, and by the time 
the maximum pressure is reached, about 1700 calories, or 12% 
of the gross heating value of the gas, has passed to the walls. 
The rate of heat loss at this point is about 10 calories per 
Sqe cM. per sec., and the mean gas temperature is 1760 deg. 
C. At 0.2 sec. from ignition the rate of heat loss is about 
3.5 calories per sqe cm. per sec., and the mean gas temperature 
is 1300 deg. C. The mean temperature is reduced in the ratio 
toe between these two points, but the rate of heat loss at 
0.2 sec. is only one-third of what it was at maximum pressure." 

Hopkinson's results from these experiments obviously 
include some of the radiation loss with the conduction losses, 
although Clerk states that only cmduction losses are included. 
Negel* 

In 1908 A. Nagel ran an elaborate series of experi- 
ments to determine the velocity of inflemmation of various 


Gases. His explosions were made in a spherical steel bomb 


‘ Mitteilungen uber Forschungsarbeiten, v. 54, 1908. 


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40 cm. in diameter. A diaphragm in communication with the 
bomb, md connected mechanically to a concave mirror, indi- 
cated the pressure developed by the explosion. Ignition was 
accomplished by means of a single jump spark occurring at the 
center of the bomb. All explosions were mde with gases 
saturated with water vapor. No maximum pressures were given 
in the report of the results, as the experimenter was merely 
interested in obtaining the velocity of inflammation. 

Nagel found that for hydrogen and air mixtures the 
inflammation velocity increased directly as the hydrogen 
content. With a constant mixture, the velocity increased 
with the pressure, the increase being greater as the mixture 
became richer. For illuminating gas and producer gas the 
velocity of inflammation also increased with the gas content. 
For these, however, at cmstant gas content, there seemed to 
be a tendency for the velocity to decrease with an increase 
of initial pressure. This effect was more nerked with weak 
mixtures than with stronger. The effect of initial temper- 
ature is not sufficiently marked to justify any definite 
ecamclusions. 


An elaborate msthematical analysis of the flame 


propagation in a spherical vessel is also given. 


From the restwlts of Hopkinson's experiments as 
quoted above it would seem that Nagel's conciusions are some- 
what in error. Hopkinson clearly showed that inflammation 


might be complete, i. e., the flame might fill the entire 


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vessel, some time before maximum pressure was attained. Nagel 
took the time from ignition (passing of the spark) to the at- 
tainnent of maximum pressure as the time of inflammation. His 
results md conclusions as to the velocity of flame propa- 
gation are therefore probably somewhat in eryror. 
Bone and others. 


In 1915 W. A. Bone, assisted by several other ex- 


perimenters, mde explosions of various hydrocarbons with 


oxygen and air. Two explosion vessels were used:- 


1) a cylindrical vessel 1" in diameter and 8" lmg. 
2) a spherical vessel 3" in diameter. 


A Petavel indicator was used to indicate the pressures de- 
veloped. 
The experiments were conducted primarily to bring 
out facts relating to the chemical transformations involved 
in the explosion process, mt the results also confirm the 
work done up to date in regard to the effect of varying the 
gas mixture and the initial pressure. 
Major W. t. David has conducted several series of 
researches on the explosions of gaseous mixtures, with special 
reference to the cooling phenomena during explosion and during 
the total cooling period. These will be discussed under 
their separate headings. 
Radiation. These experiments were mde with a 
cylindrical explosion vessel 4 cm. in diameter and 30 cm. 


long, and a Hopkinson indicator was used to record the 


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explosion pressures, A platinum bolometer, connected in a 
galvenomenter circuit, was placed in front of a diathermanous 
fluorite window at one end of the vessel. The change in re- 
Sistance of the bolometer as indicated by the galvanometer in- 
dicated the amount of radiant heat falling on the platinum 
surface. The interior of the vessel was painted with a dull 
black paint, which absorbed practically all the radiant heat 
falling on it, or wes sihver plated and polished. 

Four series of experiments were comucted with mix- 
tures of Cambridge coal gas md air, mamely:- 9.8% and 15% in 
the black walled vessel, and 13% md 15% in the vessel with 
polished walls. The general conclusions obtained from the 
experiments in the black walled vessel were as follows:- 

1) The total amount of heat lost to the walls 

of the vessel by radiation up to the time of maximum 


pressure is approximately proportional to the third 


power of the maximum absolute temperature, multiplied 


by the time of the explosion. 

2) The total radiant heat lost to the walls 
during the explosion md the subsequent cooling is 
about 25% of the heat of combustion of the ges. 

3) The emission of radiation at all times var- 
ies with the temperature ed with the time from ig- 
nition. 

4) In weak mixtures (and probably also in 


stronger mixtures) the rate at which radiation is 


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emitted is = maximum some time before the attainment 


of maximum pressure, and probably occurs at the time 


when the flame fills the vessel. 


5) Weak mixtures radiate much mre powerfully in 


the initial stages of choling than do strong mixtures 


when they have cooled to the same temperature as the 


weaker. 


6) Carbon dioxide emits radiation about twice 


as strongly as does an equal volume of water vapor 


at the same temerature. 


7) The total heat lost by radiation up to the 


time of maximum pressure decreases as the initial 


pressure of the mixture is increased. 


8) Denser mixtures radiate heat much mre strongly 


than thinner mixtures, especially at the instant of 


maximum pressure and in the initial stages of cooling. 


The emission varies approximately as the square root 


of the density. 


One of David's sets of curves, showing pressure, 


temperature, , total radiation, and radiation per sq. cme of 


eylinder area is shown in Fig. ll. The relation of radiation 


to the size of the 


loss in calories per sq. cm. per sec. 


vessel and the initial pressure is shown in Fig. lc. This 


radiation loss, after correcting for absorption, varies with 


the temperature nearly in accordance with Planck's formula 


for a single wave of length 35.6 p- At high temperatures 


rated eat hs Ol CBR 


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(1800 to 2400 deg. C.) the Planck formula reduces approxi- 
mately to a variation with the square of the absolute tem- 
perature. 

In a later article David discussed the calculation 
of the results from observed data, md derives the formulas 
on which the curves given above are based. In another arti- 
cle he discusses the radiation from a mass of brning gas 
from a theoretical standpoint, and draws various conclusions 
in regard to the wave length of the radiation emitted, ete. 

Effect of COs on the Mixture. LExperiments were 
made in the same apparatus when the mixture was diluted with 
carbon dioxide instead of the nitrogen of the air. Lower 
explosion pressures were developed in each case than in the 
former experinents. David attributes this differeme to 

1) the greater specific heat of COo at high 
temperatures. 

2) dissociation phenomena, leaving a considerable 
amount of gas unburned at the time of the maximum 
pressure. 

The theoretical analysis of Appendix I of this disctission 


confirms these hypotheses. 


Conduction. David has recently made experiments 


to determine the loss of heat to the walls of the explosion 
vessel by conduction. His original explosion apparatus was 
used, with the sddition of a polished silver grid which was 


mounted on a piece of linoleum, and placed on the end wall of 


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the vessel. This grid was connected in a galvanometer 
circuit in such a way that the deflections of the galvanometer 
indicated the temperature of the grid, md consequently the 
conduction loss to the erea covered by the grid. The total 
loss by conduction was taken es the amount of heat used in 
heating the grid (as indicated by the galvamometer) plus the 
amount passing through the grid to the linoleum backing. This 
last amount was calculated from a power series formula with 
empirical coefficients. 
It was found that the loss by conduction varied 

over different parts of the vessel, md therefore a position 
was selected for the grid which gave a mean loss over the 
entire vessel. 

3 The loss of heat up to the time of maximum pressure 


by conduction, in percent of the heat of combustion of the 


gas mixture used, is given in the following table: - 


Percent gas Percent loss 

15.0 5.1 

12.4 5.5 

a.7 11.0 
The greater time of explosion for the weaker mixtures over- 
balances the effect of the high temperatures attained in the 
strong mixtures, end increases the heat loss over that ob- 
served for the strong mixtures. 

At 0.5 sec. after ignition the 15% rixture has lost 

by conduction ebout 38% of its heat of combustion. The 12.4% 


mixture has at the same time lost about 34% and the 9.7% mix- 


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54 


ture about 28% of their respective heats of combustion. The 
curves in Fig. 15 show the rate at which heat loss by con- 
duction is proceeding while cooling is going om. The weaker 
mixtures in the initisl stages of cooling lose heat mre 
rapidly than the stronger mixtures when they have cooled to 
the same temperature. This is probably due to cmvection 
currents, which are more vigorous in the early stages of 
cooling than in the latter. 

No mention is made in David's report of eny cor- 
rection for radiant heat absorbed having been applied to the 
values obtained from the silver grid experiments. Polished 
silver absorbs about 4% of the radiant heat falling on it} 
even when highly polished. It is probable that the silver 
grid actually in use absorbed more than this amount, owing to 
the deposition of soot on the grid. It therefore appears 
that David's results should be corrected for this discrepancy. 
Miscellaneous. 

The experimenters mentioned in the preceding para- 
graphs have produced the most trustworthy results, so far as 
the measurements of the physical phenomena involved in the 
explosions of gaseous mixtures are concerned. A cons iderable 


amount of literature has been devoted tothe chemical and 


mathematical sides of the problem, however, and many interesting 


we ee ee ee ee ee eee ee ee ee ee re ee ee ee ee ee ee ee ee ee ee ee Ee 


i Landolt & Bornstein--Physikalisch-Chemische Tubellen, 
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and important results have been obtained. 
A number of other exper imental researches slong the 


same lines as those mentioned above are available, anmmng which 


are those of Pier, Langen, Falk, and Dixon, mt their work, for 


the most part, is merely a confirmation cf the results pre- 


viously discussed. 


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III. DESCRIPTION OF APPARATUS 


The original apparatus was designed and built by 
Prof. Ae P. Kratz during the year 1915. After being used for 
& number of experiments (1 to 171) work was suspended on the 
problem until September, 1919, at which time the writer was 
assigned to the problem. 

The apparatus was then reconstructed. Tests 172 
to £01 inclusive were mde with the apparatus reconstructed 
substantially as originally built. 

The original apparatus cmsisted of a cast steel 
base plate with fow removable vessels or heads, designed to 
be bolted to the base plate. The heads were respectively 
cylindrical, conical, hemispherical, and “L-head" shaped, 
(patterned after the common L-head gasoline engine cylinder). 
The actwal dimensions and proportions of the heads are shown 
in Fig. 14. The head selected for use was placed on the 
base plate, with a thin paper gasket around the rim, and 


fastened in place by eight 14" cap screws. The heads were 


very heavily built, being designed to withstand safely an 


explosion pressure of 2500 pounds per square inch. A 4" 
two bladed fan, driven by 2 shaft through the cemter of the 


base plate, afforded a means of stirring up the mixture 


oa ye re & sche 


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42 


before and during explosion. A hole for the ignition plug 
and holes for intake and exhaust piping, as well as for the 
indicator, were provided in each head, as shown in Fig. 14. 

The indicator, screwed into the side of the head in 
use, is perhaps the most important pert of the apparatus. An 
optical instrumnt was adopted as being the only type suitable 
for use in such an investigation. A drawing of the original 
indicator is shown in Fig. 15. The diaphragm indicator was 
adopted as being most accurate and convenient. 

The indicator diaphragm, (D) 3/64" thick, and having 
a semicircular corrugation emecentric with the outside circum- 
ference of the disc, wes cut from a bar of chrome-vanadium 
steel. The corrugation was introduced in order to insure a 
straight line calibration for the indicator, to give the dia- 
phragm greater flexibility, and to prevent slippage of the 
parts when heavily loaded. A small threaded projection at 
the center of the diaphragm gave a means of connecting the 
mirror system. A thin steel spring (S), bent at right angles 
and supported by a small standard (R)} screwed to the base bar 
(B) was joined rigidly to the diaphragm by two small clamp 
nuts on the threaded projection JP). A small piece (approxi- 
mately 1/16" in diameter) of concave mirror (M) was cemented 
to the spring (S) at such a distance from the support as was 
found by trial to give a proper deflection. A small enclosed 
arc lamp projected a beam of light on the mirror, whence it 


was reflected to the photographic paper, held on a longitudi- 


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nally moving slide. The arc lamp and slide were placed at 
proper distances from the mirror to give a clear-cut image of 
the crater of the arc on the photographic paper, which gave a 
narrow black line for the record. The mirror used was a small 
piece cut from & concave galvanometer mirror of 1 mwter radius 


of curvature, 


This indicator gave very satisfactory results when 
adjusted, but was very inconvenient to adjust, as the mirror 
could not be moved to give the proper position of the spot of 
light on the photographic papr. The indicator was also af- 
fected by any vibrations occurring in the hezvy base bar (B). 
The vibration of heavy machinery in the building made these 
vibrations very noticeable in the base «nd explosion lines. 
The indicator was therefore remodeled as will be described 
later. 


The explosion vessels had two connections diametri- 


cally opposite for the admission ed exhaustion of the air 


and gas. Heavy steel needle valves, made from solid bars, 
were used to open or close the ports for admission or ex- 
haus tion. 
Gas ond Air Measurement 

The gas used in all the experiments, except some 
few tests with hydrogen, was illuminating gas, taken directly 
from the city mains. A storage tank of 10 cu. ft. capacity 
was filled with the gas, md several complete series of ex- 


plosions mde with the same tankful. In this way a cmstant 


a TORE RE Se 


(pont ea Be 


hee, el be 
+ 5 7 y rat ¥ 
_ ~~ i ie a “a _— Syl ae 
“sd Godby f Shige 


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watt atdd HT , Latsied eae one eh 


45 


gas composition was insured, except as the unavoidable de- 
terioration of the gas occurred. The gas was stored over 
water, and hence was saturated in all experiments. 

The scheme originally employed to secure the de- 
sired mixture of gas and air and to introduce the mixture int 
the vessel was that of measuring the partial pressures of the 
gas and air. A mercury manomter (Fig. 16) fitted with a 
special electrical contact device, and reading to 0.01", was 
connected to the gas and air piping system for measuring 
these partial pressures. The accuracy of measurement atteined 
with the electrical contact on the manometer insured a maxi- 
mum error of 0.05% in the air gas ratio. 

Ignition. 

Ignition was accomplished by means of a #" induction 
coil supplied with current from a 6 volt storage battery. For 
some few explosions ignition was effected by an Atwater -Kent 
Unisparker, driven slowly by the mparatus controlling the 
motion of the slide for the photographic paper. The Unisparker, 
however, proved rather unsatisfactory at these low Speeds, as 
it often failed to fire the charge, and was therefore discarded, 
and the induction coil again used. A contact fixed on the 
slide carrying the paper closed the induction coil circuit 
at a time to give ignition at the desired point on the photo- 
graphic record. A mica insulated spark plug with a 0.035" 
gap, communicated the spark to the charge. A small spark 


gap, in series with the plug, was placed close to the photo- 


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Fig. 16 
/Tercury /lanomerer 


47 


graphic paper on the moving slide. The passage of the spark 


across this gap, and at the same instant across the plug in the 
vessel, gave a dot on the photographic paper. By measuri ng 
the horizontal distance from this dot to the perpendicular 
erected from the base line through the position of the spot of 
light from the indicator when at rest, and laying off this dis- 
tance on each explosion card, the exact time at which the spark 
passed, with reference to the beginning of the rise of pres- 
sure, could be determined. Usually from 6 to 10 separate dis- 
charges occurred while the slide contact remained closed. These 
discharges occupied a time of about 0.1 sec. 
Paper Motion. 

The photographic paper was mounted on a slide (§) 
which moved longitudinally in a frame bolted to the base bar (B) 
(Pig. 17). The slide was givenits motion by a "cmstant 
speed” device, similar to that used on vertical blue printing 
machines. The speed of this device was not constant, and hence 
the time scale of the diagram was somewhat distorted. As the 
Slide, having mnsiderable inertia, required an appreciable 
time to attain the speed set by the constant speed device. This 
defect was remedied when the apparatus was remodeled. 
Time Kecord. 

A record of time was obtained from an electrically 
driven tuning fork mounted close to the indicator. A small 


concave mirror cemented to one leg of the fork received a beam 


of light from the arc lamp, and reflected it to the photo- 


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graphic paper, tracing a wave with a frequency of 100 vibra- 
tions per second on the paper when the fork was in vibration. 

The method of calculating the time of explosion from 
this record will be illustrated later. 

Recording Paper. 

The photographic paper originally used was Eastman 
B.. wy G. bromide paper, cut into strips 2" x11". Later it 
was found advisable to use a special Eastman recording paper 
(known as “Eastman Recording Paper No. 1"). This pape was 
coated with an emulsion very nearly as fast as the standard 
Kodak film emulsion, and good results were obtained. 

The photographic records were developed immediately 
after taking them in the standard MQ developer recommended by 
the Eastman Kodak company. 

New Apparatus. 

The apparatw as originally built was remodeled in 

1919-1920 and some new features added. The principal change 


effected was in the design of the indicator. The heavy base 


bar (B) was removed entirely, and the spring carrying the 


mirror was clamped directly to the indicator body. A small 
strut communicated the motion of the diaphragm to the spring. 
A set of two concentric rings formed the base to which the 

spring was clamped. These rings could be turned to any de- 
sired position and clamped, thus giving a range of adjustment 
of the plane of motion of the indicator mirror to any desired 


engle. Vertical adjustment was provided for by the use of 


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long studs to which the mirror spring was clamped. Pho to- 


graphic views of the indicator as remodeled are shown in Fig. 18. 


This instrument proved to be very satisfactory, since 
it was free from all effects due to vibrations and jars, md 


had ample opportunity for adjustment. The indicator was cali- 


brated by comparison with a special dead weight tester con- 


nected in the air line to the explosion vessel. A high pressure 


air reservoir, carrying 500 lb. per sq. in., provided a smrce 
of high pressures for calibration. The instrument was cali- 
bre ted when screwed into place on the explosion vessel, and no 


adjustment of it was mide during any series of experiments. 


The calibration was checked several times during each series, 
and from the results obtained from the calibrations, it is evi- 
dent that the instrunent retains its adjustment and calibration 
characteristics for long periods of time. A sample calibra- 
tion curve is shown in Fig. 19. 

It appears from certain mathematical calculations as 
to the natural period of vibration of the indicator that the 
instrum nt easily followed the most rapid explosion occurring 


in any of the work done in this investigation. 


The paper motion was also renmodeled. The longi- 
tudinally moving slide was discarded, and a revolving drum 
11" in circumfereme was substituted. The drum was driven 
through e worm gear reduction by a small D. &. motor, which was 
capable of being regulated to a speed proper for the explosion 


record to be take@m. A contact attached on the circumference 


ee 


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Fig. 18. Photograph of 


No 
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- 
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53 


of the drum completed the primary circuit of the induction coil 
to give ignition at the proper position of the drum. 

This drum motion was much mre satisfactory than the 
slide which wes formerly used. The drum could be started 
some time before mking the explosion, the firing switch could 
then be closed, and the card taken with the drum running at a 
constant speed. 

The method of measuring the gas to be admitted to 
the explosion vessel was changed. A 100 cc. gas burette, 
graduated to 0.1 cc. was connected to the gas line and to the 


explosion vessel. The volume of gas required to give any 


desired air-gas ratio was calculated from the volume of the 


vessel and the piping through which the gas was admitted, and 
preper corrections were made for clenges of partial pressure, 
etc. This method was more accurate than the partial pressure 
method of securing the desired mixture. Some minor changes 
were also made in the gas and air piping. 

The new apparatus proved to be exceedingly conven - 
ient and reliable, and the greater part of the results herein 
given were obtained with it. A photograph of the complete 
apparatus is shown in Fig. <O and a detailed photograph of the 
conical explosion vessel with all connections is shown in Fig. 
21. 

The gas and air piping is illustrated in Fig. Zé and 


the wiring diagram for the ignition system in Fig. 23. 


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54 


Explosion Vessel. 


of Conical 


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+“ 


IV. PROCEDURE IN MAKING AN EXPLOSION 


Before any explosions were made in a new series of 
tests, a considerable amount of gas was blown out through the 
supply pipes to insure a fresh supply to the vessel. The 
vessel was then thoroughly swept out with compressed air, dur- 
ing which time the fan was kept running. After three or four 
minutes, the air was shut off, the exhaust vaive (E) (Fig. 22) 
was closed, the vacuum pump stsarted, and the vessel exhausted 
to abmt 10" of mercury absolute pressure. After shutting off 
the vacuum pump, the gas was measured in from the burette as 
desired. When the proper volume of gas had been admitted, the 
exhaust valve was opened, and air filled the vessel and piping 
up to atmospheric pressure. The needle valves {N) were then 
closed, and the desired mixture of gas and air in the vessel 
was ready for explosion. 


In case the partial pressure method of obtaining the 


desired mixture was employed, the procedure was modified some- 


what. The zero reading of the manometer was recorded, and 
the platinum contact point (P) (Fig. 16) was set, by means of 
the vernier, at a position to give the desired partial pres- 
sure of the air. The vessel was then evacuated until the 


mercury in the manometer fell below the contact point. Air 


: ; a 
E . oo as ae re Re, ee 
| a 
ik 7 : 
; ; Pu 
- a 7 ot - py) ” i" 
d 3 "f ea oyap! eee a Gey ey Sao LTR ys ne - 
“ 5 as = 
1 a } ae , iad a % f ash one 2 oy 
' ae 
| | ~luoeaom att of (iow anes 
aft d w Som: Soper AES2 
i : sci Ke £ , mae Se yt Rat 4 
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ib 
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: ae 
* 4 “=o Cat hak... Detter cesart eh 
| 
! a ak : - al Ga ye fa ; —<—F ° om 
a yw TR oO kets Pe. OUD eae) 
J - 
+a Stier a} GHEE ha boupaeet se ewes 
i wr 
- iat ¥ = \ 
‘ fi 2ee 26 cole ts 
a as | if’ Dee Las PESOS 
i we (2) 257 y eLhoesd eff i eek: 
Lo an au TO WSL 
+ Fe ey EE) ts Sar al Se 
; ar ey ae oar vey 
t PEO raty ay MSOs Ss fie ac 
“ a “ ‘ 4 
, t ow ws Pe wee ) af $e, 
hie Jp h bed ai, of? OVE oto ia & 
o)..) (eye + cate 


id » ed 8 a, a 


59 


was permitted to leak in slowly until the buzzer in the man- 
ometer circuit indicated that the proper partial pressure of 
the air had been reached. The gas valve was then opened, and 
gas was admitted until atmospheric pressure was obtained in 
the vessel. 

The fan in the vessel was run about 600 rpm. during 
the admission of the gas (except as specially noted) in order 
to insure thorough mixing of the charge. It was also run 
during explosion for certain series of tests. 

After placing the photographic paper on the drum and 
starting the driving motor, the arc light wes started and a 
zero (or atmospheric) pressure line traced on the paper. The 
tuning fork was then set in vibration, the shutter in front 
of the paper was opened, and the firing switch (F) (Fig. 23) 


was closed. At the next closing of the cmtact on the drum, 


the primary circuit of the induction coil was completed, the 


Spark was passed in the cylinder, md the charge fired. The 
photographic record was then removed and developed as pre- 
viously described. 

Fig. 24 is a reproduction of an actual explosion 
card, with the necessary lines and dimensions for determining 
the maximum explosion pressure and the time of explosion. 

The line A-A is the zero, or atmospheric pressure 
line traced before explosion. OP is a perpendicular to this 


zero line, passing through the highest point on the pressure 


~ af 
v= 7 


~ > p ’ im, al M4 
' wai kee e238. 070 Pe 
: ‘de Sa 
e. i . 4 
F; d 
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: t See 
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wane ee ae > = = * Saat 
a a r * 
“J F . ee ees 
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curve. The distance OP then represents the maximum pressure 


developed by the explosion, and by reference to the calibration 
curve (one of which is shown in Fig. 19) the eactuel pressure 

in pounds per square inch mey be determined. The dots at the 
Tight hand end of the card were produced by the gmall series 
Spark gap, pleced close to the paper. The dot at the left of 
the group merks the first spark passed in the vessel. A cer- 
tein distance (obtained by measurenent on the drum itself) is 
daid off from this dot, parallel to the zero pressure line, 
giving the point X as the ignition point. The horizontal 

di stence XO is then a meesure of the time of explosion. 

The sine wave traced by the tuning fork is situated 
elong the top of the card. The tuning fork used had an actual 
rete of vibration (by calibration) of 98 vibrations per second. 

The following notation is used in connection with 
the determination of the time of explosion. 

Ny an arbitrary number of vibrations, usually 10. 
number of vibrations of fork per second. 


number of vibrations of fork contained in the dis- 
tance L (which is equal to XO). 


XO (representing the time of explosion). 


horizontel distance covered by Ny vibrations of the 
fork. 


the time of explosion in seconds. 


oe ~~ see he a 


Selly. wee » yotiiete? © > =m ee oe 


7 aa "iG Fd a ay 


® - > 


Ors 37, ‘sonnet ia ¢ 


o fc? SF ete Tos we hae ng CoE 
‘ 


_ ee 
Lt fig iwcalays 


catia Dal Ci ae ae oti 


2 - 
* ~ Pp Ed = Maes 
4 a 3 = "i * and oiye J 
n" , , al : 
> a rs ee r 
r ‘ 
rt ~ a: ” 
. 2 J 2 a a wee Fase (as 
, : 
« ae = } 
M } eS x 
ae, Paes 50 i le Dick py ae 
PF 
- 
¥ is & 
$e i os at Le Li 
I 7 * aay te 
= G ew id > gl 
. 
; = + Salk wee. 3 ‘ 
tis ¥i- Of OeES 
- “) = me = - a 


oF. 
is eo Se. 
Ware 8 oi. Pe i st Vad © ELE 
a wits ‘4 
. ~ ie) = ? f3 


wets be Te tae ler s 


“co ; =) 
= < J ty % bi in c< i : 
r as $ 
. ra " z ao) be e - 
es t ys : « » ,bh . 
. , L ; - a, oF eT a a. 


LSeiSi7 ee Me bosses cu he tui 


If Ny is taken as 10 vibrations and Ng is 98 vibrations per 
second, 


ft 


«20 
9 Ty 


Hence by measuring L and Li, and proceeding with the above 
calculations, the time of explosion may be determined as 
accurately as the measurement of the various distances can 


be made. 


Se ena ee 


%, 
bcs 
bay 
“ 
« 


q 
ist 
i> 
as 
Lets 
er 


Fld 
wt ® 
fy 


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ae = Piel oF a~ 

a i ty ee 

. re » & Ss 

s is2) 


s ae al 
wa t 
. me os + { 
3 : c - 

w ma 

¥ et Pa at 
a c 
in ra a 

a x = me 

io 7 =" £3 

+ = ee 4 

. 4 +a 

t ay a 

* got: ' ~~ 

2 Gi na = 

5 sad oO < Gr 

9 ta 

i : ae ay 
™ 9 a 

oO > 3) 

7 en <7 

ree) M mj 

7 Ly z 

. ry = 


= 


ag =< 


a 


63 


Ve. RESULTS 


General. 

All the results of this investigation were obteined 
from explosions made with illuminating gas md air. The gas 
was taken directly from the city mains. Owing to the fact 
that the experiments on the "I-head" vessel and some experi- 
ments on the cylindrical vessel were made in 1915, and explo- 
sions were made in the rest of the heads in 1921, a consider- 
able difference existed between the analyses of the gas used 


at the two different periods. A set of gas analyses follows: 


Analysis October 8, 19157 


: COe oe e s e a ® . 1.8% 
6) e es e es e ° e 2.0 

c Gea re «0 fs «lat 

CH, es e e . e e ote ol 

Dee ar ees ss 4059 

Tlluminants ... 7.5 

Ne ee » J e e es s 9.2 

100.0 


Approximate heating value: 453 Btu. per cu. ft. 


———— ee Se ee eee ee ee ee ee em em ee mee me ee me ee me Se ee ee ee 


* This analysis is approximate only. 


ort +f 
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eee ‘ we - = Sec : —- car, th ® = ee 
“SSH to How r iB t, as. GO Rea? Sis Ga G Be ogy fie 
pesy Soy cae Re peagtenk OO test og: a 
~ if 7 ie ' ; 
1awelios, seevinws umn Ise 4 -a6c.tnegy 1NBSe 
“9 a" 
= af af Si 
2 j 
: - 
a —— 5 an : ‘ 7 4 
TIRE 0 ep) om ea 
Wine , 2 = & & 
earn | r + = # * 
ru 
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ras ‘ 
woNes & s ¢ . 
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ci a 5 2 . 3%. ier) 2 ORY 


ae. eee Se oe ee? ee ee ma ae A des A i a So ye le a 


64 


Analysis November 13, 1920. 


pe OC iseiicials 6-62 [e? ie 86 
) enh 6/6) ee 67) 8 od 
eran 
CoHo. 6 « -\ayy 6 . e@ 5.4 
CoH,. Ore. Gof .0 Ve 54 
CoH. ee © e@ e# «@ e 6.2 
c2ié. vs see 11666 
woe. 4 ns BB 
No ° ee «#0 4 


Approximate heating value: 787 Btu. per cu. ft. 


From a comparison of the approximate heating values 
of the two samples of gas it is evident that a considerable 
difference may exist between explosions rm with the different 
lots of gas. The 1915 gas was much richer in hydrogen than 
the 1921 ges, and hence had a higher rate of inflammation. 
The gas was stored over water in all cases, and hence was 
saturated in the the teste made. 


vem ee eee a eee 


The method of procedure in testing any one of the 


heads was to run several series of explosions, under various 


conditions of ignition, turbulence, etc. Each series con- 
sisted of a number of explosions made with different mixtures 
of gas and air, ranging from the richest to the leanest mix- 
ture that could be exploded. No attemt was made to deter-~ 
mine accurately the limits of inflammability of the gas, but 
the mixtures were varied until the mixture denoted by the 


next "half unit" higher or lower in the air gas ratio failed 


OBeS oe ee 


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t 


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— a i _ + » — te, 
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oct “cd hetoaes sorieia ene tite Sede A 

* * r . . % i i - 
HOLE? OCLT29 Sey time off nL tome t ae zody Bi 


to explode. 


Curves of maximum pressure and time of explosion 


plotted against air-gas ratio are given for each different 


head, and under several different conditions for each head. 


An index of the series of tests follows. 


Vessel 


Cylindrical 
L-head 
tT 


Cylindrical 
Ww 


womMIamA OWE 


Conical 
w 


nv 
t 


Hemispherical 


Explosions of hydrogen and air were also made in the 
conical vessel for the purpose of obtaining a check on a 
method of calculating the explosion pressure. These explo- 
sions will be discussed separately. 


Series l. 


This series was run on the cylindrical head, with 
ignition at the center and flush with the upper surface of 
the vessel. The gas was admitted without stirring and was 
exploded sfter standing five or ten minutes. 


The curves (Fig. 25) are typical of all experiments 


ana 


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r 1SS8 CSE soe eee ret 3s ee ror r : t 
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one t tt 4 tt —}—! {to-r by ep 14 14 + ~} 44 - -Ed- 
i Eitri eu rrhitt rr a tts ++ +44 r t-te ¥ t+ im ae Sasa ae 
‘ pitt a} : L _L it +4 t t . : Hl 
r | Lt ! a i | t / < er.” ve J t t + = ---Pg uy 
t 4 ttott { phi +44 + 5 ic a bp iz ort V a Li ty at Ba i a= Ami 
Cy 5 SSSR REESE See iS aeeen eal / i ee tenes oe ‘di es wd Coot im fs an a is a oa 
| TE it ; [ ttt { ; / i aeas chen / / 
S . ay rt - + + + if : L _ ~ } = ; 
t + + 4 Lt 4 re ai | it T trTi t rt : i t rtt rit Tt Weis T 
a~athe : @ SSRee bees 5 1 Rowe hee TT Fs i rey Tipp tae eS Crriery a Coe EE Ee itt 
T I : + ae ae a 2m Omi ee 3 
| t | oe | Th i : rrit +t tt r }--4-4. 444-1} 4 ae + : + 1 : thts 
y } = | t tt 
= — -_t-—_-_1 - - t ease LL jeer It L Ly a I as oe es ee . 


ct 


67 


of this sort. The air-gas ratio giving the highest explosion 
pressure is 3.9 to 1, a value considerably less than the t heo- 
retical ratio (about 6 to 1). This is accounted for by the 
fact that the large amount of neutral gases present when a 

6 to 1 mixture is fired keep down the maximum pressure much 
pelow the value obtained when insufficient oxygen is present. 
a The point at an air-gas ratio of 11.54 is very probably in 

| error on account of the difficulty of measuring the low de- 
flections of the indicator, and on account of the fact that no 
well defined maximum pressure occurs for the explosion of so 


q lean a mixture. (See Fig. 2). 


The maximum pressure developed in this series was 

| 92.5 lb. per sq. in. gage, a value checking rather closely with 
Clerk's value of 91.0 lb. per sc. in. for am explosion of 
Oldham gas and air. The time of explosion was practically 

| the same as in the determinations of Clerk, namely about 0.05 
second, 


Series &. 


This series {Fig. 26) was run on the L-head vessel, 
with ignition flush with the upper surface of the vessel and 
i] at the center of the main chamber. No stirring at any time 
| was used. 

Ae compared with Series 1, in’the cylindrical head, 
the advantage of the former is apparent. The decrease of 
| maximum pressure with the L-head vessel is due to the greater 


surface exposed to the hot gases during explosion, and to the 


= 
= 


Ste 


ea emma 5 = tem aa 
a ee 


———— 
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a 


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a 
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Pa 
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we te 
we 
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aqouvié of? setae 
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i ees trois [SPU ee Pee 
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‘ = id HO Ait Sa Cee 
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rT, ay b t - t ‘ 


69 


fact that the time of explosion is shorter in the cylindrical 


head by about 0.01 sec., thus reducing the opportunity for 


heat loss. 


It is possible that complete canbustion does not 


take plece in the L-head vessel when ignition occurs in the 


main chamber, as the flame may be checked and cooled consider- 


ably by passing into the narrow opening of the valve chamber. 


Series & and 3. 


Series 3 (Fig. 27) was run under the same conditions 


as Series 2, except that the fan in the vessel was run during 


explosion. A comparison of Series 2 and 3 is shown in Fig. 28. 


The higher explosion pressures and the shorter 


times of explosion produced in Series 3 are very noticeable, 


especially with the leaner mixtures. The turbulence occasioned 


by the fan brings the inflammable gas in contact with the air 


much more rapidly and thoroughly than in Series 2, where no 


stirring was employed. The higher rate of inflammation in 


Series 3 reduces the heat loss during the time of explosion, 


and hence a higher maximum pressure is produced. 


Series 4 and 5. 


Series 4 and 5 (Figs. 29 and 30) were run on the 


L-head vessel, ignition occurring at the center of the valve 


chamber, and flush with the upper surface of the vessel. For 


Series 4 no stirring of the mixture was used, and for Series 


5 the mixture was stirred during explosion. 


An increase of maximum pressure is attained by the 


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74. 


use of the fan during explosion, as my be seen from Fig. Sl. 


The influance of turbulence of the mixture during the explosion 


period in producing a shorter time of explosion is very evident, 


especially with the leaner mixtures. 
Series 6 and 7. 

These series were run under the same conditions as 
Series 4 and 5, except that ignition was pmwduced simultan- 
eously in the main chamber and in the valve chamber (the two 
Spark plugs being placed in series), 

The same general form of curves (Figs 32 and 33) 
were obtained from this series as from Series 4 md 5. The 
difference in the times of explosion with and without the 
fan running is very noticeable, especially with the leaner 
mixtures. This is due to the action of the fm in producing 
a more intimate mixture of the gas and air molecules. As the 
mixture approaches more closely the theoretical air-gas ratio 
(65 or 8 to 1) the effect of stirring the mixture in producing 
amore intimate mixture is not so evident, and the times of 
explosion with and without stirring approach each other more 
closely. The pressure curves also approach each other more 


closely at mixtures near the theoretical, showing that the 


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increase in pressure when the mixture was stirred during ex- 
Plosion was due to the more intimate mixture of the gas and 
air molecules, rather than to any effect of increasing the 
velocity of inflammation by turbulence alone. 

Comparison of Series 1, &, 4, and 6. 

A comparison of these Series (Fig. 35) shows the 
higher explosion pressure produced with the cylindrical head. 
This is due to the smaller surface exposed in the cylindrical 
head as compared with the surface exposed in the L-head. 

Fig. 35 also shows that ignition in the center of the main 
chamber of the L-heed vessel gives the highest maximum pressure 
of any of the different ignition schemes employed with the 
L-head. The curves for ignition at the center and in the 


valve chamber simultaneously and in the valve chamber alone 


show conclusively the influence of the narrow valve chamber 


in cooling the flame immediately after ignition. The time 
curves also corroborate the above cmeclusions. 
Series 6 and 9. 

Series 8 and 9 (Figs. 36 and 37) were run on the 
cylindrical head, as in Series l. Series 8 and 9, however, 
were run in 1921, ad on account of the difference in the 
Characteristics of the gas used, the results differ from the 
results obtained in 1915, using the same vessel. As no 
accurate analysis of the gas used in 1915 is evailable, no 
actual comarison of the qualities of the gases can be made. 


Series 8 and 9, run respectively without stirring and with 


a 


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stirring during explosion, are campared in Fig. 38. The in- 
crease of maximum pressure with the fan running is very mrked. 
Series 10 and ll. 

These series (Figs. 39 and 40) were mde in the 
conical head, with ignition occurring at the vertex of the 
cone. Series 10 was run with the fan in operation during 
the admission of the gas, and Series 11 with the fan running 
during both admission md explosion. 

The usual increase of maximum pressure when the mix- 
ture was stirred during explosion is found by a comparison of 
Series 10 and ll. (Fig. 41). 

Series 12 and ld. 

These series (Figs. 42 and 43) were made in the 
conical head, with ignition three inches down from the vertex 
of the cone, and on the axis. Series 12 was run witwut 
stirring of the mixture, end Series 13 with stirring. Ignition 
was accomplished by a spark plug having long points, with the 
seme gap length as used in the plug usually employed. 

An inerease of maximum pressure is found when the 


mixture was stirred during explosion (Fig. 44). 


Comparison of Series 9, 10, 11, and le. 


A comparison of Series 9, 10, 11, and 12 (Fig. 45) 
leads to several cmclusions relating to the decrease of 
Maximum pressure caused by heat loss. 

When ignition occurs at the vertex of the cme, a 


higher maximum pressure was found in all cases than when 


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ignition occurred three inches down from the vertex. This 
difference occurred only when the mixture was not being 
stirred during explosion. When the fan was in operation 
during the explosion, the two pressure curves coincided. It 
is probable that a pressure wave was started when ignition 
occurred at the vertex, and that it advanced smoothly down 
the cone, expanding as though through a nogzle. This pressure 
Wave causes higher explosion pressures to exist that if ig- 
nition occurred three inches down from the vertex, in which 
case the pressure wave would not be as easily set up, owing 
to the lack of symmetry of the vessel abouwt the ignition 
point. The operation of the fan during explosion breaks up 
any pressure wave, and hence the same explosion pressures 
were obtained for the two different ignition positions when 
the fan was running during explosion. 

It is evident from the time curves that the time of 
explosion differs considerably for the two positions of ig- 
nition, especially in the series in which the fan was run 


during explosion. The maximum pressures, however, are the 


same. This would indicate thet the heat loss up to the time 


of maximum pressure is approximately the same in the two 
series, even though the tines of explosion are quite different. 
It is possible, of course, that some pressure wave effect 

was set up even with the fan running. This would tend to 
counteract the increased heat loss occasioned by the longer 


time of explosion. 


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Series 14. 

This series was run in the hemispherical head, with 
ignition occuwring at the to of the vessel. No stirring 
of the mixture was employed during explosion. The results 
are plotted in Fig. 46. 


In order to compare the L-head series (run in 1915) 
with the other series (run in 1921), Series 8 on the cylin- 
drical head, was taken as the basis. The difference of the 
pressures between Series 1 and &@ was taken for various air-gas 
ratios, md laid off from the curve of Series 8 (which was 


run under the same conditions as Series 1). This gave an 


approximate “equivalent curve" representing the pressures 


developed if the 1921 gas had been used in the L-head vessel. 

The-curves showing maximum pressure for the four 
heads, using various air-gas ratios, are given in Pig. 47. 
The series thus compared were all run without any stirring 
of the mixture during explosion. 

The marked advantage of the hemispherical head in 
producing high maximum pressures is evident from the curves. 

The maximum explosion pressures produced in the 
four heads may be compared with the ratio of superficial 


area to the volume of the respective vessels. 


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Ratio A/V Max. Pressure 


Hemispherical head 0.69 90.0 


Cylindrical ¥ 1.24 84.0 


Conical i" 1.34 83.0 


L- " 1.62 75.0 


These results are plotted in Fig. 48. The cooling influence 


of the different wall areas is very noticeable from this 


a PS tO a ee 
. 


curve, 


Cooling after Explosion. 


After the attainment of the maximum pressure the 


aN tia a tt me oe 


mixture cools at a rate depending on 


at acter 


Es a tO II a Oe «I ti i A a a an A I pc 


1) the air-gas ratio. 
2) the character of the walls of the vessel. 
3) the ratio of surface to volume of the vessel. 


In Fig. 49 the cooling curves for mixtures of approximately 


6 parts of air to 1 of gas are shown. These curves were 


constructed directly from the cooling curves on the indicator 


diagrams taken on the various heads. The initial temperature 


in each case was taken as 2912 deg. F. Allowance was made 


in these calculations for the reduction in volume of the gases 


after combustion. 


In Fig. 50 are plotted curves of temperature drop 


in 0.2 sec. and 0.5 sec. (from the initial temerature 2912 


deg. F.) against the ratio of surface to volume for each of 


It will be 


the four vessels used in this investigatim. 


noted that three points fall on a straight line. One point 


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(derived from the cooling of mixtures in the cmical head) 
shows & smaller drop in temperature than would be expected 
from the values teken from the other vessels. The inner 
surface of the concial head was much cleaner and more polished 
than the other heads used, which were rusted and blackened 
considerably. It is probable therefore that the conical 
head reflected a considerable amount of the radiant heat 
falling on the walls, and hence the mixtures cooled more 
slowly in this head than in the others. The agreement of 
the three points m the straight line seems to substantiate 
the linear relation of temperature drop in a given time to 


the ratio of surface to wiume. 


Hydrogen-Air Explosions 
Mixtures of hydrogen and air were exploded in the 


conical vessel under a number of different conditions of 
ignition and turbulence, in order to study the heat loss 


during the time of explosion. Three mixtures were used, namely:- 


1) + 505 + 1.91Mp 


2) 2 + Op + 5.8 

$) 41202 + 5.710 
For some of the explosions a special "sSix-gap" spark plug 
was used, which had six gaps of about 0.03" each, spaced about 
one inch apart. This plug, when in place, gave a series of 
Sparks along the axis of the cone, at intervals from the 
vertex to the base. Very rapid ignition was accomplished by 


the use of this plug in conjunction with the fan. 


— Ss 


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ana es eS 


Each of the above mixtures was exploded under the 


following condi tions;- 


Ignition at vertex Fan not running. 
¥ " x running. 

" 3 in. down not running. 

¥ " iy running. 

with 6-gap plug not running, 


# : " running. 


Some further minor variations were made in the ignition con- 
ditions in special cases. 
A table of the above described results follows on 


the next page. 


. 


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Results of Hydrogen-Air Explosions. 


Time of explosion 


Test No. Max. Press. 
, seconds. 


Lb. per Sde in. 


Hp + $05 + 1.9Ne 


0.0175 
0.0146 
0.0098 
0.0161 
0.0126 
0.0095 
0.0148 


0.0077 
0.0251 
0.0148 
0.0105 


0.0970 
0.0920 
0.0227 
0.0544 
0.0527 


= 


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103 


The experiments just described furnish data on the 
maximum pressures developed and the times of explosion of 
mixtures of hydrogen and air, with the mixture in any one of 
the three series held constant, and ignition and turtmlence 
conditions varied to obtain various times of explosion and 
corresponding maximum pressures, 

If the maximum pressure is plotted against the time, 
curves as in Figs. 51, 52, amd 53 are obtained. If the line 
through the series of points in my one of these curves is 
prolonged to intersect with the axis of pressure, (or zero 


time) the point of intersection will give the theoretical 


maximum pressure which would be developed if no heat loss to 


the walls of the vessel occurred. 

Hopkins states that the heat loss varies with the 

square root of the time from ignition. This statement appears 
to be cmfirmed from the shape of the curves in Figs. 51, 
52, and 53. The curve in Fig. 51 is practically a straight 
line, as the mixture exploded very rapidly. This line cor- 
responds to the first part of the “square root curve" cited 
by Hopkinson. 

The maximum pressures, assuming no heat loss during 


explosion, have been calculated (Appendix I) as follovs;- 


Mixture with 302 101.1 lb. per sq. in. gage. 
, Ps 92 "6.4." 
" " 120. &5.4°°% 


7 


The curve through the observed points clecks the calculated 


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es 
Lf 
r 
LJ 
LJ 
J 
Ss 
= 
# 
a 
ane 


o 
2. oe 


= 


ety! 


- 


ies a 


SESS S2Se88 5 
BEREU SHANE EE ‘SB 
Sen 06 s0nnE oe 


H 
ee 


aa 


is 


Rees! 


oe 
ie 
ce ws 
- a 
: 


=e) 


Pet ; Ty i 
ie ei eee 4 
Poet 
tit 
t faa HH 


- - 
a ’ 
ciattet ttt em 
segcees 1S om i 


- aie 


FREER EEE EEE EE 


PELE Cee eet 


St 


seeeagaeee 


waaneuRane 
SSE ze Fe aaae 


point closely in each case. 
The minimum loss of pressure due to cooling during 


explosion is as follows; - 


Mixture with #0. 12.9% loss. 


21.2 , 


140. 14.6 =" 


Such large losses are not usually found, but these 
are due to the small volume of the vessel used and the rapid 
cooling, as shown in Fig. 49, as compared with the vessels 
used by other experimenters. 

It is probable that much further data on the heat 
loss during explosion could be obtained by a study of ex~ 
plosions such as those just discussed. By making the walls 
of the vessel totally absorbing or partially reflecting the 
radiation losses might be separated out md a study made of 


the conduction and radiation losses separately. 


v5ute os Va Sentadde ed. f [ine ean: 


‘hole 8 Bae Sar folder ES ‘od vega 


Pity. ey et 
ay 
veast fou “Sit fo sider sp ol 


Chew feoeupic ote Re ete Oh we 


of 


sero heen bie - 
shah vedo tole hed oan? & 


i > oe 
; a 
ive? Ee — SBeegee Ig i 8s ie es 


Ont, LSB ae, ° > etd onde iss 


t 
~ 
* 
¢ 
* 
~ % 
- — 


VI. CONCLUSIONS 


From the results of this investigation the following 
conclusions may be drawn. 

1) The conclusions of other experimenters as to the in- 
fluence of the air-gas ratio on the maximum pressure and 
the time of explosion have been confirmed. 

2) In general, the effect of turbulence of the mixture 
during explosion is to bring about an increase of maximum 
pressure and a decrease of the time of explosion. 

3) The effect of turbulence is largely that of producing 
amore intimate mixture of the gas and air molecules 
before combustion, rather than that of projecting the 
flame into the unburned parts of the gas mixture. 

4) The position of the spark gap (in vessels patterned 
after the combustion spaces in use in gas engines) has a 
considerable influence on the rate of inflammation and 


on the maximum pressures 


5) There is evidence in certain cases of the formation 


of pressure waves (of different character than trues 
explosions waves) which travel smoothly through the vessel 
and produce higher maximum pressures than if inflammation 
proceeded in the ordinary way. 


6) The maximum pressure and time of exlosion are mater- 


mad 


i 


SROLEULONGS 6 3T 


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ially affected by the shape of the explosion vessel, the 
primary cause of this effect being the variation in the 
ratio of surface to volume for the different vessels. 
7) The combustion of the gases in any pocket in the vessel 
(such as the valve chamber in the L-head vessel) is often 
incomplete, due to the cooling effect of the walls, which 
reduces the maximum pressure. 
8) The cooling of the mixture in any given time after 
explosion and maximum pressure varies directly with the 
ratio of surface to volume for the explosion vessel, 
other conditions being constant. 
9) Radiation evidently plays an important part in the 
cooling of the mixture, as a change in the cheracter of 
the inner surface of the walls of the vessel causes a 
considerable change in the cooling curve. 
10) Hopkinson's statement that the heat loss to the walls 
of the aaube varies as the square root of the time from 
ignition has been confirmed for the loss during the exp- 


losion period. 


11) A method of evaluating the loss of heat during explo- 


Sion has been demonstrated. 

12) Calculations of the maximum pressure, based on the 
properties of the gas mixture, have been checked by ex- 
perimental results for the explosions of hydrogen and air. 


mixtures. 


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TABLE OF RESULTS 
OF 


EXPLOSIONS OF ILLUMINATING GAs AND AIR 


eTR0GZR GO ee 


SiS GHA BAe crt ine 


Cylindrical head. 
No stirring. 
Ignition at top. 


Test No. Air-gas ratio Max. Press. Time of expl. 
Lb. per sq. in. SCC. 


48 321 87.1 0.0510 
49 5677 92.5 - 0438 
50 4.06 92.0 -0366 
561 4.99 84.1 ©0450 
6.10 75.4 0668 

7,03 66.2 2 0999 

8.60 52.0 02590 

9.43 44.5 «4010 

11.54 7.0 6280 

5.68 86.5 00044 

4.06 88 .5 ©0370 

4.59 87.5 »0563 


Line To enid -CG0TS kas 
. 068 ofl .f@ eer. ,dt 


CLBO. 0 . £,%8 


vv 

i ah ae ” 

bag 2 
- a = 


 SBe0, 


L-head e 
No stirring. 
Ignition at cemter. 


Test No. Air-gas ratio Mex. Press. Time of expl. 
Lb. per sq. in. ' $ec. 


62 5e91 82.0 O,---- 
63 4.97 76.5 0.0471 
5.79 67.65 0549 
Yas BF ..9 ‘6o= 2" 
8.41 48.0 en--- 
8.19 491 om--- 
9.71 36.6 - 3460 
10.65 21.0 7220 
£83 ~~-- ema 
526 71.0 - 1830 
5.64 78.8 -0578 
4.16 82.2 0381 
4.87 80.5 - 0453 
5.80 68.0 ~06387 
7.17 57.0 ~1218 
8.49 47.0 22163 
10.57 21.0 «7450 
5.87 68.1 ©0623 
7.52 5E.5 °1455 
8.8 40.1 ©4250 
9.99 21.1 * 7600 
8.09 48.0 .0@070 
9.03 40.1 °4180 


ee ee 


ScSC, 
YRag. 0.8% 
Sisf. 0.46 
Sore. 0.5 
O8LT. 0, 


mee Ty) i . $e 
iG Ab f . & 2 L¢ : 
meas e ce: fal . 
OS Cie toe 
GUST » Le f8 
t © s+ i. oe 
OBlp, L.O8 
ish 
= 
* 
o - 
. 7 on 


L-~head. 
Stirring during explosion. 
Ignition at center. 


Test No. § Air-gas ratio Mex. Press. Time of expl. 
lb. per eq. in. sec. 


118 3.03 80.5 0.1265 
5.51 83. - 0588 
4.20 87 0 00223 
4.66 68.0 0187 
4.99 84.1 0204 
6.11 74.1 
7 Qt 66.0 
8.23 59 .0 
9,40 50.8 

10.27 48.1 
11.87 ---- 
8.39 59 .0 
4.70 88.0 
11.00 ---- 
3ek5 80.5 


L-hea a ° 
No stirring. 
Ignition in valve chamber. 


Test No. Air-gas ratio Max. Presse Time’of expl. 
; lb. per sq. in. sec. 


3.18 61.5 0.0776 
3.61 70.8 O55? 
4.06 71.0 60474 
4.96 13.3 . 0504 
5.68 66.1 .0760 
7.06 55.0 .1455 
9.26 41.5 3280 
9.64 35." 5100 

10.81 12.5 .7670 
2.91 58.0 23790 
4.14 12.5 0450 
6.93 BE 2 1179 
4.04 1464 0431 
6.03 365 22970 
9412 36.5 4620 

10.10 £1.0 ee 

10.20 82.1 .8070 

11.03 6.0 6860 


ee 


Series 5 


L-head . : 
Stirring during explosion. 
Ignition in valve chember. 


Test No. Air-gas ratio Max. Pre 


lb. per sq. 


136 3.06 74.1 
137 3.29 78.7 
138 4.14 84.2 
139 4.76 84.2 
140 5.05 85.2 
141 6.04 74.1 
142 7.35 65.3 
14 8.32 57.0 
144 9.46 51.5 
145 10.44 49.1 


Series 6 


No stirring. 
Ignition in center and valve chember 


146 
147 
148 
149 
150 
-- 251 
L5eé 
153 
154 
155 


74.1 
75.1 
76.& 
61.5 
Wael 
6543 
65.5 
41.9 
65.7 
E736 


os « e @ 
oe Sos 


e e . 


ie] 
LON s Wao 


= 
OWOMVAOOP A OO 
[ae 
v 


on 
oO 


QO. 


0 


0455 
0547 
~0196 
0204" 
~0209 
20278 
0441 
0528 
20728 
0973 


»0538 
~O502 
0471 
0453 
~O501 
~9705 
~ 1690 
22940 
04495 
~ 5890 


is 
cy 2 
Of Se 
we GD 


cy 


i‘ 


Todo ov lav boo Tetnee: 


¥ 
- 


. 
—,. 


¢; 
« 
b 


id 


Lehbead. 
Stirring during explosion. 
Ignition at center and valve chamber. 


Test No. Air-ges ratio Max. Presa. Time of expl. 
lb. per sq. in. sec. 


156 08 78.7 0.0532 
157 549 85.1 00224 
158 $.18 . 8810 -O151 
159 4.78 87 .0 «0175 
160 4.70 87 .0 02282 
161 5.20 | 83.8 » ORS 
162 6.21 72.5 08438 
163 7.07 65.8 0390 
164 8.51 57.0 0548 
165 9.28 51.5 0693 
166 10.40 45 6 ~ 1482 
167 11.14 19.5 2660 


Series 


Cylinecrical head. 
No stirring. 
Ignition at top center. 


£06 4,17 
209 5.29 
£11 6.25 
ele 6.55 
£14 9257 


& i <> 


Y getueg! 


: Pes a sect 
+ SEO enw far Sha 


roe Lee otey “ens | 


me ee. Me 
a 


= 


& Goit 


Series 2 


Cylindrical head. 
Stirring during explosion. 
Ignition at top center. 


Test No. Air-gas ratio Max. Press. Time of expl. 
lb. per Sq. in. sec. 


223 3.13 91.0 0.046 
225 4.17 92.0 2026 
R26 5.29 89.0 0933 
227 6.25 78.5 0044 
228 7.29 66.5 --- 
250 9.57 49.0 185 


231 10.42 bia a ied 
232 11.47 Stent 
233 2.08 3 
234 2.61 83.5 
237 8.53 60.0 
238 9.90 aa 


Series 10 


Conical head. 
No stirring. 
Ignition at vertex. 


£74 3.138 
B75 £61 
£76 4.17 
“B77 Beal 
278 05 
a79 7429 
£80 8.53 


» Reet + eee 
pa 54 | 550 4 aif L 


GG 
UG 


9.86 
C 208 
(at 
88 
aE 
a OF 


— a 


117 


Series 11 


Conical head. 
Stirring during explosion. 
Ignition at vertex. 


Test Lo. Air-gas ratio Max. Press. Time of expl. 
lb. per gq. in. sec. 
329 2.08 87.0 0.0700 
330 2.61 91.5 ° 0280 
331 5.13 93.8 ©0390 
332 3.65 90.38 20380 
333 4.17 83.6 ~0516 
354 5.21 75.5 00496 
335 6.26 66.6 ~O810 
336 7.29 56.5 1360 


Conical head. 
No stirring. 
Ignition 3" from vertex. 


306 2.61 78.0 0.040 
307 4.17 7365 0079 
308 5.13 81.6 e056 
310 5.e1 65.5 . #138 
211 6.25 53.5 0271 
31 7.29 41.2 550 
313 8.56 mene ae 
514 £08 60.0 136 


515 7.81 7.0 ee 


Conical head. 
Stirring during explosion. 
Ignition 3" from vertex. 


Test No. Air-gas ratio Max. Press. Tine of expl. 
lb. per sq. in. SEC. 


316 £08 80.35 0.088 
517 2-61 91.5 0044 
518 5013 o28 0036 
319 5-65 91.5 038 
320 4,17 87.0 2034 
325 7.29 59.5 —« eL19 
324 7.81 52.0 167 
325 8.85 4.4.8 0267 
326 9.57 . 5.0 -=- 
327 5.al 79.0 0064 
228 6.25 68.0 088 


Series 14 


Hemispkerical head. 
No stirring. 
Ignition at top. 


350 
351 
552 
353 
354 
355 
S56 
257 
358 
359. 
360 


ols 


, 
aw os 
VN 


APPENDIX I 


CALCULATION OF EXPLOSION PRESSURES 


OF 
HYDROGEN AND AIR MIXTURES 


SaVBAMAS ROTATE BO | 


, SSG Sh as 


APPENDIX I 


CALCULATIONS OF EXPLOSION PRESSURES OF HYDROGEN AND AIR 


In the following discussion the theoretical expl- 


osion pressures developed by mixtures of hydrogen with var-— 


ious amounts of air will be calculated. 

The equations and constants employed in the cal-— 
culations are taken from a thesis by G. T. Felbeck, entitled, 
"A Mathematical Treatment to Determine the Temperature and 

Extent of Combustion in the Gas Engine." Yhe writer is 
indebted to Mr. Felbeck for the material taken from his 
thesis. 


In order to calculate the maximum pressure pro— 


duced in the explosion of any inflammable gas mixture, it is 


necessary to take into account three factors: 


1) The heat of combustion of the mixture). 

2) The variation of the specific heat with temperature. 

3) The dissociation of the products of the combustion 
into the initial constituents, thus rendering the 
reaction incomplete. 


The mixture is assumed to be in a state of 
chemical equilibrium at the instant of attaining maximum 
pressure. 


The following notation will be used in this 


Discussion: 


? 


- 
’ 
» 


sais rt 


eITLWMOLLO 
P 1% 
> 5 
4 > ~ 
pn ® 
o od £83 
nor 
+ * 
‘ e 
ar ¢uasad 
8 
iio be 
ie o. 
, 
' 
S 
he 
. 
= 
30 io 


oo 


Ag RIE ERG “WoreosaE 90 asory, r 
+ 


2 


temperature at equilibrium, deg. F. abs. 

progress of the reaction. 

maximum pressure (at equilibrium) lb. per sq. in. abs. 
initial mixture, mols. 


mixture at equilibrium, mols. 

mean molar specific heat of diatomic gases, 

mean molar specific heat of hydrogen, 

initial temperature of mixture, deg. F. abs. 
lower heating value of mixture at the temperature 
T, in Btu. per mol at constant pressure. 

initial energy of mixture. 


N n Cd 


En = =< Be yl pM) Ca 


< 


energy of mixture at equilibrium (or maximum pressure 
equilibrium constant for the reaction. 
= number of mols of oxygen present. 


BoA ea ce 
uo] 


The general method of procedure demands two 


equations involving the two unknown variables x and T, 
By equating the energies of the mixture before 


explosion and at the time of equilibrium, we get 


and 


By inserting the usual expressions for specific heats and 


such constants as may be determined by the mixture, we get 
(m—1)y,T + ys! = (m-1)y,T, - Y¥ele 


Ay (at T deg.) 


By substituting various values of T we may calculate corre- 


sponding values of x. 


The qquilibrium constant Ky is a function of the 


temperature and of x. It is defined in the hydrogen reaction as= 


‘hoo 


< 


a eee 
fer 
&» -h * 

fi . 
\ 
aa" ae 
5 P 
a 
cal 
any 
~ 
é 
~— 

ss * 

~ 

* - 
; 7 
x -- 

jeu 
>» 
§& 


Pa 


4 
7 


4 


Ln | 


77 


= 


where n is the number of mols of oxygen present in the ori- 


ginal mixture. Ky may be expressed in terms of x by setting 


up expressions for the partial pressures of the various gases 


and substituting them in the above equation. From the re- 


sults of a number of experimenters' work, Ky is given as: 


102100 


4.578 log KS = 7 


—- €.2637 log T + 0.000236 T 
#1 0,0338-10 © T* + 1.1 


Thus Ky may be calculated for any given temperature. After 
substituting the constants as determined by the mixture, and 


simplifying, we get 


x i - 1 P, 
log 7% [n-%) = log K, + allog 7. * «log TI (2) 


. 
By substituting values of T we may calculate corresponding 
values of x. If Equations (1) and (2) are plotted, their 
point of intersection gives the values of x and T which will 
satisfy both equations. 

The explosion pressure F may then be determined 


from T as follows: 


oe @ ck ae 


atta eff at Janaetgq Aeyyyo Yo ven sy) sedauted ee 
mS 


aiiise ad °x to saved oF Reaeevane ae Accel Hes 
dean epottan- ates esduesere te! Faq ait 104 


eon% of Jae62 2’0de,e07 ok aedt 


ovis @f <§ .aow 'pvedeeekesqes Ie redmue ; 
“s : ie te rd 


n 1} 


Oortat 
| 3 io ”. | net | ee ae ae <'_h pela 


2 ~~ 
rf + *t ®pf-sen0.0 + "oe 
ee ‘.stutetequeal newt? a2 70 7 bate lootee aan Bo 


“hes a wmixte e472" <q bentetades& ae evinsieses 


vathaogaes ties Glaelusiso yam on ? 20 dase seitod 
viedt ~bsitofe ove (8) bre. (Le bnot feng? ST) 
{irw dardw TT ibeew xO esa lev af aovid agit or i 


> 41O.t, hy a) 


teyeldab sq wed2 vat q @7022074 notsoigxue od? . 


The specific heat equations for the diatomic gases 


follows: 


Vag 2.0 + 0.2778 T 
¥, = @.51 + 0.25 T 
The lower heating value of hydrogen at constant volume is 


taken as 102930 Btu. per mol. 


Case Il. Ho- * 50, +1.9N, 


Original mixture Mixture at equilibrium 


Hs 1 mol H,O x mols 
Of ie lx " 
Ny O.5x °" 
m eS es 
3.4 — 0.5x mols. 


Energy equation= 


2.4y,0 Yst = Delve = Ys'¢ 
H 


Vv 


xX = 


Substituting values of T, we get 


T 4000 4200 4400 4€00 4800 5000 
x 675 «fal W772 <827 .884 645 


Equilibrium equation= 


a | . P 
Wee -4e- (oneceaseiO*> = leg K,+ sl logs ar + log T] 


Substituting values of T, we get 
iE 4000 4400 4800 5000 
x 988 975 954 ~9a9 


Plotting these two sets of values (Fig. 54), the 


of intersection are found to be 


values at the point 


0.940 
4983 °F. abs. 


x 
di 


From this value of T we calculate P as follows: 


14.4°49838 
535 


PlS.o.ib. per. sq, ny “abs. 


101.1. Ib. per 8q% in gage. 


Case II. He vt 0. 3+ 22. ON 


energy and equilibrium equations we find 


1.000 
S667crs abs, 

Pes. OC O_ib.. sper.sq..in. abs. 
¥75.6 lb. per.sq.. ink gage. 


a 
i 


H, + 1.50, + 5.7N, 


energy and equilibrium equations 


x = 1.000 
LP o=s2G42° nhs “abs. 
PP =i60.6 1b... per. sq. in abs. 


55.4 1b. per sq. in gage. 


~ > 
Cr ae 
% 
7 
ty 


iaczsananane 
RARHH SRR! aapeaee ERReS 


eee ae Eu et at eure at uel eet 


rt i PH a 
; HH Hh . 


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sbepett 


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j 


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20R00hs eee 
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